Mars Global Surveyor
Mars Orbiter Camera

June 2001: Mars Opposition and Equinox

MGS MOC Release No. MOC2-285, 12 June 2001

Animation of simulated Earth-based Views

Note: A caption describing this release is below the "Simulated Earth-based
views"---please scroll down to caption. This release contains numerous
additional pictures of Mars. To see these, please
click on each of the pictures below to view a simulated Space Telescope
image, then click on each simulated Space Telescope view for the
full-resolution Mars Global Surveyor image upon which each simulation
was based.

Prior to the Mariner 4 flyby in 1965, all we knew about Mars came from
Earth-based telescopic observations. At best, Mars is a challenging
object to observe, due to its small size, low contrast, and
turbulence in Earth's atmosphere. The best times to see the planet
are around its closest approaches to Earth, which occur near
"opposition", when the two planets are roughly in a line on one side
of the Sun. This occurs about every 26 months, when Mars can appear
to grow (in the night sky) to as large as about 20 arc-seconds in size.
(20 arc-seconds is about the
apparent size of a dime seen from 190 meters, or about the length of two football fields, away; it is about the
size of a crater 40 kilometers (25 miles) in diameter on the Moon.)

In 2001, Mars is at opposition on June 13-14 and makes its closest
approach to Earth on June 21, when it is about 67 million kilometers
(~42 million miles) away and subtends 20.8 arc-seconds in the sky.
For observers in the northern hemisphere, it can be seen as a bright
(magnitude -2) red object, low in the southern sky near the
constellation Scorpius, in the evening.
Southern hemisphere observers have a better view, as Mars is higher in
the sky from that vantage. (See
http://www.skypub.com/sights/moonplanets/0105marsreturn.shtml
for more information.)

In homage to the many dedicated professional and amateur observers who
have monitored Mars during its closest approaches over the years (see,
for example, http://www.lpl.arizona.edu/~rhill/alpo/mars.html)
we thought it would be fun to simulate the view from Earth using
recent images from the Mars Global Surveyor (MGS) spacecraft orbiting
400 kilometers (249 miles) above the red planet. The data were
acquired by MOC between June 5 and June 7, 2001. The Mars images were
synthesized from a set of daily global map observations. Because MGS
orbits Mars once every two hours, MGS can see the entire planet in
twelve pole-to-pole image swaths. The images shown here were taken by
the Mars Orbiter Camera (MOC) Wide Angle cameras and digitally wrapped
onto a sphere. These cameras are "fisheye" lenses with a focal length
of about 11 mm and an f/number of about f/6.5. The lenses image onto
linear CCDs (Charge-Coupled Devices) with 3456 7-micron-square pixels.
Earth-based telescopes often invert (top becomes bottom and vice versa) what is being viewed; the MOC simulations are presented here with south at the top to match this inversion.
Clicking on each of the "Simulate Earth-based views," above, will take
you first to a simulation of what the Hubble Space Telescope might see
from Earth orbit at this time, and clicking on the Simulated Hubble
view will provide the original MGS MOC image mosaic.

Not only is Mars at opposition June 13-14, 2001, and making its closest
approach to Earth since 1988 on June 21st, on June 17-18 Mars will be
at equinox, with the southern hemisphere turning to spring and the
nothern hemisphere begins autumn. The diagrams below illustrate the
opposition and equinox configurations of Mars.

Like Earth, Mars is tilted on its axis and thus experiences a change of
seasons as it orbits the Sun. A Martian year is about 687 Earth days
long. In this diagram, the Sun is represented by a yellow circle at the
center. On June 17-18, 2001, Mars will be at the position shown just right
of center, "Equinox: Southern Spring/Northern Fall".

Mars opposition occurs appromately once every 26 months when Earth, Mars,
and the Sun are all in a line with Earth between Mars and the Sun. In
our night sky, Mars is brightest during opposition; in June 2001 it
can be found in the vicinity of the constellations Scorpius and
Sagittarius. The large yellowish feature in this diagram is the Sun.

Mars opposition in 2001 occurs June 13-14. The planet's closest approach
to Earth takes place several days later, on June 21st.

Malin Space Science Systems and the California Institute of
Technology built the MOC using spare hardware from the Mars Observer
mission. MSSS operates the camera from its facilities in San Diego,
CA. The Jet Propulsion Laboratory's Mars Surveyor Operations Project
operates the Mars Global Surveyor spacecraft with its industrial
partner, Lockheed Martin Astronautics, from facilities in Pasadena, CA
and Denver, CO.